This invention relates generally to heterostructure diode injection lasers and more particularly to stabilized filamentary lasing in a thin region of a nonplanar active layer of a double heterostructure (DH) injection laser.
It has been known to reduce the width of the filamentary area of the active layer of a double heterostructure injection laser. One manner of controlling active layer thicknesses is by providing a groove or channel structure in the laser substrate prior to LPE, MBE or OM-CVD growth processes for producing the junction layers, such as, disclosed in U.S. Pat. No. 3,978,428. Another manner of controlling active layer thickness is by providing a mesa structure on the laser substrate prior to LPE, MBE or OM-CVD growth processes as exemplified in U.S. Pat. 4,185,256.
We have discovered that in the case of channel substrate structured lasers, that some of those devices that were fabricated exhibited lasing preference in an area above the upper edge of the etched channel in the active layer. Lasing in this tapered or thin region or sector of the active layer provided control of the lowest order transverse mode. Stabilized lowest order mode operation is believed to be achieved because of the constricted nature of the active layer in this region of the laser and the employment of asymmetric pumping, i.e., positioning of the stripe geometry substantially over this constricted filamentary region of the active layer. Other higher order modes are not developed because they would extend into areas of decreased gain with attendent higher radiation and absorbsion losses.